Ferrite circulator having three mutually coupled coils coupled to the ferrite material



Nov. 15, 1966 R. w. ROBERTS, JR 3,236,201

FERRITE CIRGULATOR HAVING THREE MUTUALLY COUPLED COILS COUPLED TO THEFERRITE MATERIAL 5 Sheets-Sheet 1 Filed April 29, 1966 INVENTOR. ROY W.ROBERTS JR.

W MM. ATTORNEYS Nov. 15, 1966 R ROBERTS, JR 3,286,201

FERRITE CIRCULATOR ING THREE MUTUALLY COUPLED COILS COUPLED TO THEFERRITE MATERIAL Filed April 29, 1966 5 Sheets-Sheet 2 INVENTOR. ROY W.ROBERTS JR.

ATTORNEYS Nov. 15, 1966 R. w. ROBERTS, JR

FERRITE CIRCULATOR HAVING THREE MUTUALLY COUPLED GOILS COUPLED TO THEFERRITE MATERIAL 5 Sheets-Sheet 5 Filed April 29, 1966 'INVENTOR. ROY w.\ROBERTS JR w WM ATTORNEYS United States Patent FERRITE CIRCULATORHAVING THREE MUTU- This application is a continuation-impart ofcopending application Serial No. 326,850, filed November 29, 1963 nowabandoned.

This invention relates generally to circulators, and more particularlyto circulators for the UHF and lower frequency ranges.

A circulator, as used herein, is an N port device where N is greaterthan 2. It has the property that when'the ports are suitably numbered 1through N, an applied input electrical signal at port 1 emerges fromport 2 with a minimum of attenuation while neglible power emerges fromthe other ports. Likewise, a signal applied to port 2 emerges from port3, etc.

Circulators have been made for several years for the microwave frequencyrange. These have taken the form of differential phase shift circulatorsand Faraday rotation circulators. Both types make use'of a ferriteelement as a non-reciprocal perturbation. Because of this, the usableband width has been limited and the size of the circulator relativelylarge.

Ferrites, as discussed in this application, include all types offerrimagnetic oxides such as substitution ferrites, spinels,perovskites, garnets, anti-ferromagnetics and hexagonal barium ferrites.These are discussed in Lax and Button, Microwave Fer-rites andF-errimagnetics, McGraw-Hill, 1962.

In recent years. considerable advances have been made in so-calledjunction ci'rculators. This class of circulator makes use of ferriteelements at the junction of three or more transmission lines. Thesedevices have considerably reduced the size of such circulators partlybecause the ferrite interaction is dominant rather than a perturbation.

These latter junction circulators consisted of a disc of ferrite locatedat the junction of three strip transmission lines. The dimensions of theferrite disc were such that the diameter was approximately equal toone-half wavelength at the operating frequency of the circulator. Theferrite acts as a resonant cavity in which electric energy is stored inthe capacitance between the stri-pline center conductor and groundplanes and magnetic energy is stored in the RF magnetic fields in theferrite. A perpendicular D.-C. magnetic field causes the permeability ofthe ferrite t-o anisotropic, thus causing non-reciprocal couplingbetween the ports. The dimensions of the ferrite disc determine theresonant frequency of the cavity which, in turn, determines theoperating frequency of the circulator. This results in a lineardependence betweencirculator diameter and wavelength.

The result of this linear relationship between the operating wavelengthand the size of the ferrite disc is that the circulator becomesextremely large at low frequencies. For example, a circulator designedto operate at 150 MHZ. has a diameter of approximately eight inches. Thelarge size of these distributed constant junction circulators makes themimpractical for use in many UHF and lower frequency range applications.The large ferrite size also results in a high cost.

It is, therefore, a general object of the present invention to provide acirculator for use in ultra high frequency and lower frequency ranges ofthe electrical frequency spectrum.

It is another object of the present invention to provide a circulatorwhich is compact and simple in construction.

3,286,201 Patented Nov. 15, 1966 It is still another object of thepresent invention to provide a circulator making use of a multiple turncircuitferrite interaction.

It is a further object of the present invention to provide a circulatorin which the function of non-reciprocity and circuit tuning areseparated.

It is a further object of the present invention to provide a circulatorwhich is broad band and inexpensive.

The foregoing and other objects of the invention will be more clearlyapparent from the following description taken in conjunction with theaccompanying drawing.

Referring to the drawing:

FIGURE 1 is a plan view, partly broken away, to show the interior of atypical circulator in accordance with the invention;

FIGURE 2 is a side elevational view of the circulator of FIGURE 1, againpartly broken away, to show the interior elements;

FIGURE 3 is a sectional view taken along the line 33 of FIGURE 2;

FIGURE 4 is a perspective view showing the multiple turn circuit ferriteinteraction arrangement;

FIGURE 5 shows the equivalent electric circuit for one connect-ion ofthe lumped circuit elements;

FIGURE 6 shows an equivalent circuit diagram for another connection ofthe lumped circuit elements;

FIGURE 7 shows an equivalent circuit diagram for a double tunedconnection of lumped circuit elements;

FIGURE 8 shows an equivalent circuit diagram for another double tunedconnection of lumped circuit elements;

FIGURE 9 shows the equivalent electrical circuit for a delta connectionof the lumped circuit elements; and

FIGURE 10 is a curve showing the circulators electn'cal properties as afunction of frequency.

Generally, in accordance with the present invention, there is provided acirculator which includes a junction of at least three transmissionlines which includes mutually coupled coils. A ferrite material isdisposed in cooperative relationship with the mutually coupled coils.Means for magnetizing the ferrite are provided to impartnon-reciprocity. Lumped capacitance is connected in each of thetransmission lines. The coils, capacitors and ferrite provide separationof the functions of non-reciprocity and circuit tuning.

The lumped constant circulator of the present invention is made up oftwo basic portions; a magnetic energy storage element and an electricalenergy storage element. These two elements interact together in such away as to resonate at the frequency of interest. The magnetic energystorage element is responsible for the nonreciprocal properties of theresulting circulator. The magnetic energy storage element consists of aferrite body on which is wound three or more coils connected together ina wye or delta configuration. A D.-C. magnetic field perpendicular tothe axis of all three coils magnetizes the ferrite body to a low lossanisotropic state considerably above (or below) the field producingferromagnetic resonance. The properties of the magnetic energy storagedevice are determined by the number of turns of wire on the windings andthe D.-C. magnetic field applied to the ferrite body.

The electric energy storage element can consist of many differentcircuit connections. For example, a simple capacitor in series with eachof the three windings gives excellent performance at narrow bandwidths.Here, the value of the capacitor is chosen such as to resonate with theinductance of the magnetic energy storage element at the desiredfrequency. Exact values of the capacitance are determined by theinductance of the magnetic energy storage device, the impedance of theinput and output circuits and the desired operating frequency of thedevice.

It is important to note that the electric energy storage element doesnot have to be located within the circulator,

but can be located remotely from the magnetic energy storage element;and, in fact can consist of parasitic capacitances existing elsewhere inthe circuit. Hence, two generalized configurations of the lumpedconstant circulator exist. In both cases, the non-reciprocal propertiesof the device are determined by the magnetic energy storage element. Thetwo configurations comprise a magnetic energy storage element alone withthe electric energy storage device being located remotely or as a partof a surrounding circuit and an integrated device in which the electricand magnetic energy storage elements are housed within a singlestructure.

FIGURE shows a typical plot of a lumped constant circulators electricalproperties as a function of frequency. It is seen that the device hastuned circuit properties and over a reasonably wide band affords a veryhigh ratio of forward to reverse attenuation. Varying the capacitiveenergy storage element would permit tuning of this device over amoderate frequency range and more complex electrical energy storageelements would give broader band performance.

Referring to FIGURES l3, a typical circulator for UHF includes spacedground planes 12 and 13. Mounting plates14, 16 and 17 of the coaxialconnectors 18, 19 and 21 are secured by screws to spaced ground planes.

The center conductors 31, 32 and 33 of each of the coaxial connectorsare each connected to a conventional radio frequency capacitor 36, 37and 38, respectively. Each of the capacitors have their other terminalconnected to one end of a coil 41, 42 and 43, respectively. Thecapacitors illustrated include a plurality of interleaved plates.However, any conventional capacitor may be used. The coils are mutuallycoupled to one another. The coils may include a plurality of turns fortight coupling or may comprise a single elongated lead portion adjacentto the ferrite for less coupling. The amount of coupling, i.e., thenumber of turns, depends upon the circuit application and the impedancedesired. The other ends of the coils or leads may be connected to oneanother to define a Y. It will be apparent to one skilled in the artthat the mutually coupled coils may also be connected in a deltaconnection, as will be presently described. The coils 41, 42 and 43shown are in the form of multiple turns wound about a ferrite wafer 46,which forms the nonreciprocal element, as will be presently described.FIG- URE 4 is an enlarged perspective view of this arrangement.

The combination of series capacitors and coils 36 41; 37, 42; and 38, 43form a tuning means whereby the circulator can be matched to theassociated transmission line.

The ground planes 12 and 13 may each include a recess or well 47 and 48,respectively, which accommodate permanent magnets 49 and 51,respectively. Cover plates 52 and 53 are disposed over the well andserve to retain the permanent magnet material 49 and 51 in the properrelationship with respect to the ferrite wafer whereby to provide afield through the ferrite material in such a direction as to give riseto the desired non-reciprocity in accordance with well known techniques.In certain instances, it may be desirable to employ magnetic materialfor the cover plates to offer a lower reluctance path for the magneticfields of the permanent magnet. For further reduction of the reluctance,side plates 60 of magnetic material may be provided to bridge the spacebetween the ground planes.

The complete assembly may be placed within a housing 56 which includesopenings for receiving the associated coaxial connectors and which mayhave a removable cover plate 58 secured by spaced screws 59.

Referring to FIGURE 5, there is schematically illustrated an equivalentelectrical circuit diagram for the circulator just described. Thevoltage generators defined by the source 61 and resistors 62 representthe signal of the circulator.

at each of the transmission lines. The arrow 63 represents thenon-reciprocal characteristic of the ferrite material, while thecapacitors and inductors correspond to those previously described andbear like reference numbers.

It is seen then that the tuning function is separated from thenon-reciprocal characteristic of the ferrite. The coils are mutuallycoupled to one another and to the ferrite.

The capacitors may be connected in shunt with the input terminals ratherthan in series therewith. This is schematically illustrated in FIGURE 6where like reference numerals refer to like parts.

In FIGURE 7, there is shown an input circuit which provides operationover a broader frequency band. This circuit, in addition to the elementspreviously described, includes a tuned circuit comprising a capacitor 66and conventional inductor 67 connected in each of the arms The tunedcircuit has one terminal grounded and the inductor connected by a tap tothe capacitance and inductance previously described. The double tuningarrangement of FIGURE 7 provides what is known in the art as doubletuning to increase the band of frequencies over which the device isoperable.

Double tuning can be provided in conjunction with a shunt circuit byintroducing a series tuned circuit. This is schematically illustrated inFIGURE 8 by the series capacitor 68 and inductor 69.

FIGURE 9 illustrates the delta connection for mutually coupled coils41a, 42a and 43a. Capacitors 36, 37 and 38 are shown connected in serieswith the associated lines. It is to be understood that the capacitorscan be connected in shunt. Further, double tuning, as previouslydescribed, may be employed.

The diameter of lumped constant junction circulators, unlike thedistributed constant circulator, is independent of frequency. Forexample an approximately /2 inch diameter ferrite disc, as definedherein, can be made to .operate over the 50 to 350 me. range with only achange and inexpensive.

in the number of turns on the ferrite and an adjustment of the D.-C.field. For circulator action, of course, a proper electric energystorage element must be provided.

Thus, there is provided a circulator which is simple The function oftuning and reciprocity are separated so as to be independentlycontrolled. This then provides a circulator which can easily be matchedsince only lumped elements need be adjusted.

I claim: 1

l.- A circulator device of the character described comprising a junctionof at least three transmission lines. mutually coupledcoils intersectingat substantially equal angles electrically connected to saidtransmission lines at said junction, ferrite material coupled to saidcoils, and means for applying a magnetic field to said ferrite material.

2. A circulator as in claim 1 additionally comprising means including acapacitor for matching said device to an associated transmission line. i

3. A circulator comprising a junction of at least three transmissionlines forming a common region, mutually coupled coils electricallyconnected to said transmission lines at said junction, .ferrite materialdisposed in said region in coupled relationship with said coils, meansfor applying a magnetic field to said ferrite material, and a capacitorconnected in series with each of the transmission lines and said coils.

4. A circulator as in'claim 3 including additionally a tuned circuitconnected to said capacitor.

5. A circulator comprising a junction of at least three transmissionlines, mutually coupled coils electrically connected to saidtransmission lines at said junction, ferrite material disposed incoupled relationship to said coils, means for applying a magneticfield'to said ferrite material, a capacitor connected between ground andsaid coilS at each of said transmission lines, and means for connectingthe transmission line between the capacitor and the coils.

6. A circulator as in claim 5 including additionally a tuned circuitconnected to said capacitor.

7. A circulator comprising a junction of at least three transmissionlines, spaced ground planes, ferrite material disposed and supported inspaced relationship with respect to said ground planes means forapplying a magnetic field to said ferrite material, mutually coupledcoils coupled to said ferrite and electrically connected to saidtransmission lines, and a capacitor electrically connected to each ofsaid transmission lines and said coils.

8. A circulator as in claim 7 in which said coils each comprise aplurality of turns of conductive material wound about said ferritematerial.

9. A circulator comprising spaced ground planes, permanent magnet meanscarried by said ground planes, a ferrite material disposed between saidground planes to receive the magnetic field from the permanent magnet,at least three transmission lines communicating with said ground planes,mutually coupled coils electrically connected to said transmissionlines, said coils being coupled to said ferrite, and a capacitorelectrically connected between each of said transmission lines and saidcoils.

10. A circulator as in claim 9 in which said coils each comprise aplurality of turns of conductive material Wound about said ferritematerial.

11. A circulator as in claim 10 including additionally magnetic materialextending between said ground planes.

12. A circulator device of the character described comprising at leastthree mutually coupled coils intersecting at substantially equal angleseach adapted to be electrically connected to an associated line, ferritematerial disposed so as to be coupled to said coils, and means forapplying a magnetic field to said magnetic material and arranged toapply the magnetic field linearly across and substantially perpendicularto the axis of said coils.

13. A device as in claim 12 wherein said coils are electricallyconnected to a common point.

14. A device as in claim 12 comprising additionally means including areactive network for matching said device to an associated line.

References Cited by the Examiner UNITED STATES PATENTS 6/1962 De Vries33324.2 1/1965 Drumheller et al 333 1.1

1. A CIRCULATOR DEVICE OF THE CHARACTER DESCRIBED COMPRISING A JUNCTIONOF AT LEAST THREE TRANSMISSION LINES, MUTUALLY COUPLED COILSINTERSECTING AT SUBSTANTIALLY EQUAL ANGLES ELECTRICALLY CONNECTED TOSAID TRANSMISSION LINES AT SAID JUNCTION, FERRITE MATERIAL COUPLED TOSAID COILS, AND MEANS FOR APPLYING A MAGNETIC FIELD TO SAID FERRITEMATERIAL.